SLVAE57B February   2021  – October 2021 LM5050-1 , LM5050-2 , LM5051 , LM66100 , LM74202-Q1 , LM74500-Q1 , LM74610-Q1 , LM74700-Q1 , LM74720-Q1 , LM74721-Q1 , LM74722-Q1 , LM7480-Q1 , LM7481-Q1 , LM76202-Q1 , SM74611 , TPS2410 , TPS2411 , TPS2412 , TPS2413 , TPS2419


  1.   Trademarks
  2. Introduction
  3. Reverse Battery Protection
    1. 2.1 Reverse Battery Protection with Schottky Diode
  4. ORing Power Supplies
  5. Reverse Battery Protection using MOSFETs
    1. 4.1 Reverse Battery Protection using P-Channel MOSFET
    2. 4.2 Input Short or supply interruption
    3. 4.3 Diode Rectification During Line Disturbance
    4. 4.4 Reverse Battery Protection using N-Channel MOSFET
  6. Reverse Polarity Protection vs Reverse Current Blocking
    1. 5.1 Reverse Polarity Protection Controller vs. Ideal Diode Controller
    2. 5.2 Performance Comparison of P-Channel and Reverse Polarity Protection Controller Based Solution
  7. What is an Ideal Diode Controller?
    1. 6.1 Linear Regulation Control Vs Hysteretic ON/OFF Control
    2. 6.2 Low Forward Conduction Loss
    3. 6.3 Fast Reverse Recovery
    4. 6.4 Very Low Shutdown Current
    5. 6.5 Fast Load Transient Response
    6. 6.6 Additional Features in Ideal Diode Controllers
      1. 6.6.1 Back-to-Back FET Driving Ideal Diode Controllers
      2. 6.6.2 Very Low Quiescent Current
      3. 6.6.3 TVSless Operation
  8. Automotive Transient protection with Ideal Diode Controllers
    1. 7.1 LM74700-Q1 with N-Channel MOSFET
    2. 7.2 Static Reverse Polarity
    3. 7.3 Dynamic Reverse Polarity
    4. 7.4 Input Micro-Short
    5. 7.5 Diode Rectification of Supply Line disturbance
  9. ORing Power Supplies with Ideal Diode Controllers
  10. Integrated Ideal Diode Solution
  11. 10Summary
  12. 11References
  13. 12Revision History

Performance Comparison of P-Channel and Reverse Polarity Protection Controller Based Solution

P-channel MOSFET based reverse polarity protection is a very commonly used scheme in industrial and automotive applications to achieve low insertion loss protection solution. A low loss reverse polarity protection solution can be realized using LM74500-Q1 with an external N-channel MOSFET to replace P-channel MOSFET based solution. LM74500-Q1 based reverse polarity protection solution offers better cold crank performance (low VIN operation) and smaller solution size compared to P-channel MOSFET based solution. Figure 5-2 compares the performance benefits of LM74500-Q1 + N-channel MOSFET over traditional P-channel MOSFET based reverse polarity protection solution.

As shown in Figure 5-2, for a given power level LM74500-Q1+ N-channel MOSFET solution can be three times smaller than a similar power rated P-channel MOSFET solution. Also as P-channel MOSFET is self biased by simply pulling it's gate pin low and thus P-channel MOSFET shows poorer cold crank performance (low VIN operation) compared to LM74500-Q1. During severe cold crank where battery voltage falls below 4 V, P-channel MOSFET series resistance increases drastically as shown in Figure 5-2. This leads to higher voltage drop across the P-channel MOSFET. Also with higher gate to source threshold (VT) this can sometimes lead to system reset due to turning off of the P-channel MOSFET. On the other side, LM74500-Q1 has excellent severe cold crank performance. LM74500-Q1 keeps external FET completely enhanced even when input voltage falls to 3.2 V during severe cold crank operation.

GUID-20210212-CA0I-VQW3-TJ2R-9VMGNX24ZQZD-low.gifFigure 5-2 Performance Comparison of P-channel MOSFET and LM74500-Q1 Based Reverse Polarity Protection Solution